brake proportioning valves questions

I agree to using the 74 proportioning valve. As said, the fixed ratio the factory used is an estimate. Once you change brake parts (rotor diameter, pad type), tires, or weight distribution, the ideal ratio changes. An adjustable proportioning valve allows you to dial it in (in a wet parking lot), but that wasn't a factory option. You can get new ones <$30, but you probably want the whole sheebang, w/ distribution block, imbalance switch, and front hold-off valve. Those cost ~$100 aftermarket. However, the factory valve you have is probably close enough.